3.1 General
The Jamuna Multipurpose Bridge is the longest bridge in Bangladesh. It was constructed over the Jamuna River, the mightiest of the three major rivers of Bangladesh, and the fifth largest in the world in terms of volumetric discharge. The bridge provides the first fixed crossing of the Jamuna River linking eastern and north- western parts of Bangladesh. The Jamuna Multipurpose Bridge is located in a seismically active region that can be subjected to moderately strong earthquakes.
Special earthquake protection devices have been used in the bridge and have been designed to resist dynamic forces due to earthquakes with peak ground acceleration as high as O.2g. In order to observe the excitation of the bridge under dynamic loading, Jamuna Multipurpose Bridge Authority installed seismic instruments on and around the Jamuna Bridge at July 2003.
3.2 Bridge Description
The main bridge is slightly curved, about 4.8 km long, prestressed concrete box-girder type, and consists of 47 nearly equal spans of 99.375 m and 2 end spans of 64.6875 m. The total width of the bridge deck is 18.5 m. The main bridge is supported by twenty-one 3-pile piers and twenty-nine 2-pile piers. There are 128 m long road approach viaducts at both the ends of the main bridge. There are six hinges (expansion joints) that separate the main bridge structure into seven modules; two end modules, four 7-span modules and a 6-span module in the middle.
The bridge consists of four lane roads with a single-track meter gauge railway and a footpath. The crossing has been designed to carry a dual two-lane carriageway, a dual gauge (broad and meter) railway, a high voltage (230 kilo volts) electrical inter-
connector, a 750 mm diameter high-pressure natural. gas pipeline and telecommunication cables. Significant features of the bridge are given in Table 3.1.
Table: 3.1 Salient features of the bridge
Length of bridge 4.8km
Length of viaduct of each side 128.0 m
Width of bridge . 18.5 m
Number of spans I 47+2
Length of each span 99.375 m
Length of end span 64.6875 m
Number of lanes 4
Number of rail-lines 1
3 Pile Pier (2500 mm OD) 21
2 PilePier(3l50 mm OD) 29
Number of Total Piers 50
Number of Total Piles 121
Tubular steel Pile Thickness 40mm t060mm
Average Length of Pile 83.0 m (72 m below river bed level)
Box girder segment length 4.0m
Absolute rake of Pile (Batter Pile) 1: 6
Pier Stem height 2.72 m to 12.04 m
The carriageways are 6.315 m wide separated by a 0.57 m width central barrier; the rail track is located along the north side of the deck. On the main bridge, electrical interconnected pylons are positioned on brackets cantilevered from the north side of the deck. Telecommunication ducts run through the box girder deck and the gas pipeline is located under the south cantilever of the box section. The height of the pier stem varies from 2.72 to 13.05 m. They are founded on concrete pile caps, whose shells were precast and filled with in-situ reinforced concrete.
3.2.1 Pile configuration
Each module of the bridge is supported on four piers supported on 2-3.15 meter diameter piles and three piers on 3-2.5 meter diameter piles, which is shown in Figure 3.1. The piles are tubular steel piles, filled with concrete. The toe levels vary from - 70.0 m MSL (Public Works Datum) to -82.0 m MSL, with a head level of 01011m MSL. Pile configuration is shown in figure 3.2 and 3.3. The thickness ofthe steel tube
varies along the length of the pile. For 2-pile system the thickness varies as 60mm (from pile cut-offupto_6.0 m MSL), 55mm (from --6.0 m MSL to -26.0 m MSL) and 50mm (From -26.0 MSL up to pile toe). And for 3-pile system the thickness varies as 50mm (from pile cut-off up to --6.0 m MSL), 45mm (from --6.0 m MSL up to- 26.0 m MSL) and 40mm (from -26.0 MSL up to pile toe). Pile caps are of precast reinforced concrete shell with in-situ reinforced concrete infill construction. They have a base level of + 11.0 m MSL, and so the piles are embedded some 7m within the caps. The pile caps carry pier stems which in turn support the bearings. Figure 3.2 and Figure 3.3 shows the general arrangement of piles.
, 73.05m '
.. r-
_6apcMll!99.375m______ ---:7 .'.?3.0~.
,26.325rn
o SciI$dm 150
L '
Figure 3.1: Typical seven-span module
SIDEELEVATION SCALE 1:250
END ELEVATION
SCALE 1:250
.- ::=-- ~ -
-
. _. ~-
, I '''0'1400
BEARING PUNTH
TYPICAL 2 PfLE PlER
PUN SCALE 1:125
Figure 3.2: General arrangement of Piles
I
I \
1
--" --- ---
i/
f \
\
,
T,
.Z'?W-
'0J"""!' J •••••
Figure 3.3: General Arrangement 00 Piles Pier
3.2.2 Pier stem
The height of the pier stem varies from 2.72 to 13.05 m. They are founded on concrete pile caps, whose shells were precast and filled with in-situ reinforced concrete. The cross-section and elevation of the pier stem are shown in Figures 3.4 and 3.5. The reinforced concrete pier stems support pier heads which contain bearings and seismic devices which allow movement of the deck under normal loading conditions but lock moment in the event of an earthquake to limit overall seismic loads through the structure and minimize damage. The hollow section of the pier stem is filled with concrete up to 3 m of its height. Cross sectional properties of pier stem are shown in Table 3.2.
Table 3.2: Cross Sectional Properties of Pier Stem
Area Moment of inertia Moment of inertia Section type
(m2) (longitudinal) (longitudinal)
(m4) (m4)
Hollow 6.84 5.85 38.42
Solid 15.0 .7.81 45.0
400mm
400~
6400mm
Figure 3.4: Cross-section of Pier Stem
Rood Level JJ'lf? :33.5Sm
O.4!lf-, .. .
~27.5m
InC!' Lever Arm
(')
-
400mm
8m y
-+17m '+14m
Figure 3.5: Elevation of the Pier Stem
3.2.3 Deck configuration
The main bridge deck is of multi-span precast prestressed post-tensioned concrete segmental construction, with a varying depth box section constructed by the balanced cantilever method. Each cantilever has 12 segments (each 4 m long), joined to a pier head unit of 2 m long at each pier and by an in-situ stitch at mid span. The deck is internally prestressed and of single box section (Figure 3.6). The width of the box section, 18.5 m, is the same for all sections but the depth of the box varies between 6.5 m at the pier top and 3.25 m at mid-span. Accordingly, area and moment of inertia both in longitudinal and transverse direction vary along the span. The segments were precast and erected using a two-span erection gantry.
MG&il Road. Road.
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